Transplantation is an exciting and rapidly expanding field of clinical medicine with great potential for curing human disease. In addition, because of its intimate association with immunology, this field provides an opportunity for fertile interaction between basic scientists and clinicians. The availability of outstanding teams of MD and PhD scientists devoted to all aspects of transplantation, from the most basic molecular level to the actual clinical transplants, make the Massachusetts General Hospital a unique environment to foster such interactions. The purpose of this research program is to train young scientists and physician scientists in basic research in a wide variety of topics related to transplantation biology with an emphasis on immunological mechanisms in a multi-disciplinary environment. Participating faculty members with diverse but complementary research interests, a successful record of collaboration, and a commitment to training young investigators, have been assembled to provide trainees with exposure to topics related to transplantation immunology including immunogenetics, tolerance induction, antigen processing and presentation, gene therapy, adhesion molecules, bone marrow transplantation (BMT), regulation of lymphocyte development, pathology of graft rejection, and xenotransplantation. The major goal of this program is to produce outstanding independent investigators capable of addressing fundamental questions in the field of transplantation. Predoctoral trainees will be selected from students currently enrolled in the Immunology Program at Harvard University's Division of Medical Sciences who express an interest in pursuing their thesis research in the field of transplantation immunology. Training for predoctoral students will take approximately 4 years. Support is requested for 3 predoctoral trainees per year, distributed between students in their 1st, 2nd 3rd, or 4th year of thesis research. Postdoctoral trainees currently holding a degree of MD, PhD, or MD/PhD will be selected based on having outstanding potential to pursue a career in research and teaching and a commitment to independent investigation Training will require 2- 3 years. Support is requested for 6 postdoctoral trainees in years 1-5.